1. Field of the Invention
The present invention relates to a method of making super-hard tools, and more particularly a method of making drills, endmills and other rotating-and-cutting tools. A method of making super-hard tools according to the present invention has a central feature in providing a super-hard tool body with a shank. The super-hard tool body is made by extrusion and sintering.
2. Description of Prior Art
As is well known, drills, endmills, reamers, or taps have different blades appropriate for the purpose, but in common, they have a straight or tapered shank at one end and a blade along the remaining length. These tools can be fixed to associated holders or chucks at their shanks. The sufficient coarsness and hardness are required for the finished surface of the shank, and at the same time, it is required that the shank be integrally connected to the blade part of the tool. In making drills, endmills, reamers, or taps, first, a super-hard rod is prepared, and the bar is cut a predetermined length. Then, a part of the predetermined length of bar is edged with the aid of diamond tool, leaving the remaining length as a shank.
This ensures that the shank is integrally connected to the edged part of the tool, and accordingly the life of such tools is extended. The manufacturing cost, however, is very high partly because of the use of diamond tools and partly became of precision and complicatedness required in providing supper-hard bars with edges or blades. The conventional method of making super-hard rotating-and-cutting tools cannot meet the demand for reduction of manufacturing cost. In an attempt to meet such demand the applicant proposed that: an appropriate additive is added to pulverized super-hard alloy; the powder is extruded into a spiral form; the spiral form is sintered; and then the sintered spiral tool body is provided with a shank at its end by: (1) inserting one end of the sintered spiral tool body in a ferrous metal cylinder and then, brazing the tool body to the cylinder; (2) filling the spiral groove of the sintered spiral tool body with a melted metal, and cool and solidify the melted metal in the spiral groove; or (3) applying pulverized ferrous metal to one end of the sintered spiral tool body with its spiral groove filled with the metal powder, and then shaping and sintering the ferrous metal covering.
This permits efficient and easy production of drills, endmills and other super-hard rotating-and-cutting tools without difficulty, but the method has following defects:
There is a great difference between thermal expansion or contraction of the sintered tool body and that of the shank, which is made of a ferrous metal. For instance, the thermal expansion or contraction of a super-hard metal powder sinter is assumed to be 1, and then that of a ferrous metal is about 2.2. In this connection if a sintered tool body provided with a shank is subjected to heating and cooling without extra remedy, there will appear a great strain between the sintered body and the shank layer. In fact, the sintered body is stretched to the shank until there appears cracks in the sintered body. Therefore, the method proposed by the applicant is difficult to be practices unless this problem is solved.